1. Field of the Invention
The invention relates to a system for detecting a signal and, more particularly, to a system for fast lock and acquisition of ultra-wideband signals.
2. Related Art
Recent advances in communications technology have enabled an emerging, revolutionary ultra-wideband technology (UWB) called impulse radio communications systems (hereinafter called impulse radio).
Impulse radio was first fully described in a series of patents, including the following, which are incorporated herein by reference: U.S. Pat. No. 4,641,317, issued Feb. 3, 1987 to Larry W. Fullerton; U.S. Pat. No. 4,813,057, issued Mar. 14, 1989 to Larry W. Fullerton; U.S. Pat. No. 4,979,186, issued Dec. 18, 1990 to Larry W. Fullerton; and U.S. Pat. No. 5,363,108, issued Nov. 8, 1994 to Larry W. Fullerton. A second generation of impulse radio patents include the following, which are incorporated herein by reference: U.S. Pat. No. 5,677,927, issued Oct. 14, 1997 to Fullerton et al.; U.S. Pat. No. 5,687,169 issued Nov. 11, 1997 to Fullerton et al.; and U.S. Pat. No. 5,832,035, issued Nov. 3, 1998 to Fullerton et al.
Use of impulse radio systems for vector modulation is described in the following, which is incorporated herein by reference: U.S. patent application Ser. No. 09/538,519, concurrently filed, entitled xe2x80x9cVector Modulation System for Wideband Impulse Radio Communications.xe2x80x9d
Basic impulse radio transmitters emit short pulses approaching a Gaussian monocycle with tightly controlled pulse-to-pulse intervals. Impulse radio systems typically use pulse position modulation, which is a form of time modulation where the value of each instantaneous sample of a modulating signal is caused to modulate the position of a pulse in time.
For impulse radio communications, the pulse-to-pulse interval is varied on a pulse-by-pulse basis by two components: an information component and a pseudo-random code component. Unlike direct sequence spread spectrum systems, the pseudo-random code for impulse radio communications is not necessary for energy spreading because the monocycle pulses themselves have an inherently wide bandwidth. Instead, the pseudo-random code of an impulse radio system is used for channelization, energy smoothing in the frequency domain, and interference suppression.
Generally speaking, an impulse radio receiver is a direct conversion receiver with a cross-correlator front end. The front end coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. The data rate of the impulse radio transmission is typically a fraction of the periodic timing signal used as a time base. Because each data bit modulates the time position of many pulses of the periodic timing signal, this yields a modulated, coded timing signal that comprises a train of identically shaped pulses for each single data bit. As an option, the impulse radio receiver can integrate multiple pulses to recover the transmitted information.
In a multi-user environment, impulse radio depends, in part, on processing gain to achieve rejection of unwanted signals. Because of the extremely high processing gain achievable with impulse radio, much higher dynamic ranges are possible than are commonly achieved with other spread spectrum methods.
When receiving an ultra-wideband signal as part of a one-way communication system (e.g., a pager) or a two-way communication system (e.g., a wireless telephone), a problem exists as to how to detect the transmitted impulse radio signal, and more particularly, how to acquire and lock on the impulse radio signal being transmitted. This problem exists independent of how the received ultra-wideband signal is used, such as in a one-way or two-way communication system.
Previous approaches to solving this problem are discussed in the following commonly owned patents, which are incorporated by reference: U.S. Pat. No. 5,832,035, issued Nov. 3, 1998 to Fullerton, and U.S. Pat. No. 5,677,927, issued Oct. 14, 1997. The present invention presents another approach to solving this problem.
An object of the invention is to provide a system for detecting an impulse radio signal.
An object of the invention is to provide a system for fast lock and acquisition of an impulse radio signal.
The above objects and advantages of the present invention are achieved by a method, a system, and an apparatus for fast lock and acquisition of ultra-wideband signals.
The method of the invention detects an impulse radio signal with the following steps: obtaining a template pulse train; obtaining a received impulse radio signal; comparing the template pulse train and the received impulse radio signal to obtain a comparison result; performing a threshold check of the comparison result; and locking on the received impulse radio signal. Additionally, the method can include performing a quick check using the template pulse train and additional received impulse radio signal. Further, the method can include performing a synchronization check of further received impulse radio signal. Moreover, the method can include performing a command check of command data of the impulse radio signal.
The apparatus of the invention includes an apparatus for implementing the method of the invention, and the system of the invention includes a system for implementing the method of the invention.
In one embodiment, the system of the invention detects an impulse radio signal and includes: an antenna; a cross-correlator; a pulse summer; a detector; a threshold comparator a lock loop filter; a controller; and a template pulse train generator. In addition, the system can include a synchronization data memory. Further, the system can include a command data memory.
Moreover, the above objects and advantages of the invention are illustrative, and not exhaustive, of those which can be achieved by the invention. Thus, these and other objects and advantages of the invention will be apparent from the description herein, both as embodied herein and as modified in view of any variations which will be apparent to those skilled in the art.